[time-nuts] Thunderbolt controllers

Mark Sims holrum at hotmail.com
Sun Jul 6 16:48:27 EDT 2008

The Thunderbolt default config is to not save the survey position.  Unless you use some software to save the position,  every time you power it up it will do a new survey.  This takes from 1 hour to several days  to complete.  After that you really don't need a controller except for peace of mind that it is working.   Mayby once or twice a week I have noticed mine going into holdover mode because of really crappy satellite geometry and signal levels.  Without a controller giving a realtime display you would never know your oscillator is undisciplined. 

A very minimal controller might be an AVR Butterfly.  It only has a 6 character display and joyswitch.  Rather not up to the task,  but dirt cheap (around 20 bucks).  It could display a minimal go/nogo type of indication.

Best is a dedicated cheap old laptop.  You can get them for 50 bucks or so with a 1024x768 full color screen, keyboard, and real serial port.  I have a nice controller program in the works that displays full unit and satellite status,  graphs the DAC voltage, temperature, OSC error,  PPS error, and Allan variances.  Allows you to control and configure the unit.   Disadvantage is size.  The Thunderbolt and power supply do fit nicely under a laptop and add an inch or so the the height.

Next best is a dedicated controller based upon the MegaDonkey microcontroller or similar device.  It has a 160x80 monochrome LCD  with a touch screen and two real serial ports (see mega-donkey.com).   Advantage is it allows the Thunderbolt/power supply/controller to be built into a single enclosure to make a stand-alone freq reference with enough display and user input resources to be quite useable.  Disadvantage compared to a cheap laptop is cost and the small display.  You would have to page though several display screens to get a full take on the unit status.  Also the graphs would not be nearly as nice and there is not enough on-chip RAM to do ADEVs, etc.  Once I get the laptop program done I'll probably do a controller on the MegaDonkey.

> I find it a good idea to design some (small?) h/w to command the
> Thunderbolt without the need of a PC. 

>>Why?  Is anything needed?

>>What happens if you just apply power with no PC?  I'd expect it would power 
>>up and self-survey and after a while, make a good clock.  I'm pretty sure 
>>mine was working correctly before I got the software working.

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